Preheat oven to 375°. Rub a 9×13 casserole dish with cold butter, rubbing it all over the bottom and up the sides.
Prepare blueberries:
Wash blueberries first and let them dry a little on a towel.
Combine blueberries with sugar, lemon, zest, and flour in a bowl. Mix it well and then spread it all evenly in the prepared baking dish.
Crisp Topping:
In a large mixing bowl, combine all dry ingredients for the oat topping and mix well, until evenly incorporated.
Pour in melted butter all over as you are mixing the topping. Mix until completely combined and crumbly.
Baking:
Spread oat topping evenly over the blueberries.
Bake for about 35 minutes, until topping is golden brown and blueberries bubble.
Video
Notes
Make it gluten free: You can use all-purpose gluten free flour to toss the blueberries and in the topping. Note that gluten free flour doesn’t stick to berries as well so toss the berries in a little bit of lemon juice first and then in flour and sugar mixture. Make sure the oats are labeled as gluten free as well.
Make it vegan: use plant-based butter to rub the pan and in the crisp topping.
Do NOT overcook this crisp! If at 35 minutes you see that the crisp isn’t quite browned and bubbling, continue cooking it for just a few more minutes, but keep a watchful eye over the oven. You don’t want to cook out too much blueberry juices or the crisp will be dry. You also don’t want to let the topping crisp too much.
As stated before, avoid frozen berries and try to use fresh. If you must use frozen ones, allow them to thaw at room temperature first, but be aware the your crisp will most likely not taste as fresh and juicy. If there is excess liquid in the bag after thawing the berries, strain it off.
Don’t use flavored or instant oats! Plain, old fashioned unflavored oats are what this recipe calls for. The oats will be flavored plentifully by the other ingredients in the topping!